Expendable disc cutout



'{i Pennsylvania Application February 21, 1955, Serial No. 489,410

- 7 2,846,544 ,BXPENDABLE DISC curou'r Wood, Jeannette, Pm, nssignor to l-T-E Circuit Breaker Company,

My invention relates to fuse cutouts and more partlcularly to an expendable disc to allow fuse tubes to vent one or both ends depending upon the fault current interrupted by the fuse.

The expendable discs of my invention can be applied to fuse cutouts of the type disclosed in copending application Serial No. 493,177, filed March 9, 1955, assigned to the assignee of the instant application.

Distribution fuse cutouts are well known and are used for the interruption of fault currents approximately at voltages from to 17 kv.

The conventional cutout comprises a fuse link which is placed in the bore of a fibre lined laminated phenolic tube in which the bore and tube length are dictated by the current and voltage rating of the cutout. The interrupting current rating can be increased by using heavier tubing and heavier recoil stops.

When one end of the fuse tube is enclosed, the cutout successfully interrupts fault currents up to the bursting strength of the fuse tube. This interrupting current rating can be increased by allowing the cutout to exhaust at both ends, thereby reducing pressure within the tube and balancing the recoil effects. Therefore, cutouts can be capable of interrupting fault currents several times greater without bursting the tube. However, if the same fuse which is open at both ends sees a low fault current in the range of 50 to 250 amperes, interruption may not take place. It is, therefore, extremely desirable to have a means which will allow a cutout to operate as a single vent device on low fault currents and as a double vent device on high fault currents.

The prior art has shown complicated schemes to accomplish this end such as pressure actuated valves and expendable caps. The previous blow out caps were nonreusable caps which were usually made of a molded phenolic material. Other caps have been used which are made of metal having a reduced wall thickness at the end of the cap. When this section blows out, the whole cap assembly must be replaced.

However, no simple inexpensive device has been offered up to this time that will allow the cutout to perform as desired.

The principle of my invention is to insert between the fuse link and the fuse cap, an expendable disc which can be of a metallic or non-metallic material so designed to have its diaphragm blow out by a predetermined fault current. Hence, by enclosing one end with a disc which will blow out on high fault current, I can accomplish double venting of the fuse tube for high current interruption and single venting of the fuse tube for low current interruption.

Furthermore, the expendable disc of my invention is so constructed as to provide shielding of the fuse cap from the hot gases associated with fault current interruption. Hence, after operation of a fuse using my novel expendable disc, only the disc proper is replaced using the same fuse cap.

; ;Unit&sees Patent 0 I can further adapt my novel expendable disc to accommodate all universal fuse links. Furthermore, I provide with my expendable-disc a drip shield to prevent moisture from entering the fuse tube.

In summary, as well as providing a fuse tube that will vent according to the fault current, my novel expendable disc is inexpensive to replace, protects the fuse cap from burns by high current arcs, is adaptable for use with all standard fuse links, and prevents moisture from entering the top of the fuse tube.

Accordingly, it is a primary object of my invention to provide an expendable disc for a fuse cutout which will allow the cutout to operate as a single vent device or a double vent device depending upon the fault current.

Another object of my invention is to provide an expendable disc for a fuse cutout which is inexpensive and easily replaceable.

Still another object of my invention is to provide an expendable disc for a fuse cutout in which the fuse cap is protected from burning by shielding the cap with a portion of the expendable disc which is preformed to extend axially past the open end of the cap and concentric to the fuse tube casting.

A still further object of my invention is to provide an expendable disc for a fuse tube cutout which prevents moisture from entering the fuse tube.

Still another object of my invention is to provide an expendable disc for fuse tube cutouts which is adaptable for use on all standard fuses.

These and other objects of my invention will be apparent from the following description when taken in connection with the drawings in which:

Figure l is a cross-sectional view of my novel expendable disc in conjunction with a fuse tube and a fuse tube cap.

Figure 2 shows a second embodiment of Figure 1.

Figure 3 shows a third embodiment of my novel expendable disc.

Figure 4 shows still another embddiment of my novel -expendable disc in conjunction with a fuse tube and a fuse tube cap.

In Figure 1, I show a cross-sectional view of one end of a fuse holder comprising a fuse tube 10 and the tube end casting 10a. The end of fuse tube 10 is sealed by my novel expendable disc 11 and expendable disc 11 is maintained in its position by fuse cap 12.

Upon the' occurrence of a fault current, the section of the diaphragm between the dotted lines of expendable disc 11 will be ruptured to thereby vent the end of fuse 10. It should be noted that in the rupture of expendable disc ll, the cap 12 will be shielded from the hot gases due to the current interruption taking place in fuse tube 10 by that portion of the expendable disc 11a remaining between fuse cap 12 and the hot gases escaping from fuse tube 10. Hence, after operation of the fuse, one merely needs to unscrew fuse cap 12 which has been protected from these hot gases, and insert a new expendable disc 11 and rescrew the complete-assembly on tube end casting 10a. The operation is simple and the expendable disc is inexpensive. The same fu'se cap 12 can be repeatedly used.

The current at which expendable disc 11 will be ruptured will be determined by the thickness of the diaphragm. For instance, for a diaphragm ,4 made of a commercial bronze, rupture of the diaphragm would occur on a particular value of current. If the diaphragm were thick and of the same material, venting would occur on currents considerably above this value. Anyone skilled in the art could easily determine the diaphragm thickness to obtain rupture of the diaphragm for a particular material with a predetermined fault current.

Patented Aug. 5 1958 thick and 3 It is therefore possible to enclose a fuse tube with expendable discshaving different current rupture ratings to allow single venting for low fault current interruptions and double venting for high fault current interruption.

In the embodiment of Figure 2, the fuse tube body and tube end casting 10a contains expendable disc 11 maintained by fuse cap 12. In Figure 2, fuse link 13 is shown as having a fuse link button 14 in engagement with expendable disc diaphragm 11. Upon rupture of the fuse link due to fault current, the section of the diaphragm between the dotted lines of expendable disc 11 will be sheared out at some predetermined current.

However, the open end of fuse cap 12 will be protected from the hot gases escaping from fuse tube 10 by the peripheral protrusion 15 of the expendable disc 11. That is, the barrier 15 is preformed in the embodiment of Figure 2.

Figure 3 shows an expendable disc 11 having a preformed barrier 15 which can be used to replace the fuse link button on fuse links that use threaded buttons such that the reduced section of the diaphragm 17 of the expendable disc 11 ruptures under current interruption. In this manner, a threaded button standard type fuse link can be converted for heavy duty operation by simply replacing the fuse link button by means of threads 16.

in the embodiment of Figure 4, I have shown anexpendable disc 11 which can be stamped from a metal sheet. The fuse cap 12 is protected from the hot gases escaping from the fuse tube 10 upon the interruption of fault current by means of barrier 15 which is an integral part of disc. It should be noted that barrier 15 extends even further upon rupture of expendable disc 11.

In each of the Figures 1 through 4, it is clear that expendable disc 11 will also prevent moisture from entering fuse tube 10. In Figure 4, for instance, any moisture which might enter between the expendable disc 11 and the fuse cap 12 will subsequently pass through threads 18 to the outside of fuse tube 10.

In summary, my novel expendable disc provides inexpensive and replaceable means for selective single or double venting of a fuse tube. I provide a predetermined barrier between the hot blast of gases associated with interruption of fault current between the fuse tube and the fuse cap after rupture of the expendable disc.

In the foregoing, I have described my invention only in connection with preferred embodiments thereof. Many variations and modifications of the principles of my invention within the scope of the description herein are obvious. Accordingly, I prefer to be bound not by the specific disclosure herein but only by the appending claims.

I claim:

I. A fuse holder being comprised of a fuse tube, a fuse tube end casting, a reusable cap and a rupturable disc; said fuse tube end casting being positioned concentric with and removably secured to said fuse tube; said rupturable disc having a cylindrical section; a portion of said cylindrical section of said rupturable disc being positioned concentric to and between said fuse tube end casting and said reusable cap; said reusable cap having a hollow cylindrical shape and being positioned external to and concentric with said fuse tube end casting; said cap being removably secured to said fuse tube end casting and providing a friction force to secure said rupturable disc in position between said fuse tube end casting and said cap and permitting said rupturable disc to enclose one end of said fuse tube; said cylindrical portion of said rupturable disc being positioned adjacent the interior surface of said cap; said cap having a portion extending above one end of said fuse tube end casting, said cylindrical portion of said rupturable disc being positioned adjscent to the entire interior surface of the portion of said cap extending above said fuse tube end casting to thereby provide a protective barrier between exhaust gases resulting from current interruption and said reusable cap; said rupturable disc being comprised of a thin metal designed to shear around the periphery at a predetermined magnitude of pressure.

2. A fuse tube cutout being comprised of a fuse tube, a fuse tube end casting, a reusable cap and a rupturable disc; said fuse tube end casting being removably secured to said fuse tube, said reusable cap being removably secured to said fuse tube end casting, said reusable cap, said fuse tube end casting and said tube being operatively positioned concentric with respect to each other; said reusable cap having a first portion extending above one end of said fuse tube end casting; said rupturable disc having a substantially cylindrical section operatively positioned concentric with and between said reusable cap and said fuse tube end casting, a portion of said cylindrical section of said rupturable disc extending over the entire internal surface of said first portion of said reusable cap to thereby provide a protective barrier forsaid reusable cap against hot gases being exhausted from said fuse tube; said rupturable disc being designed to shear around the periphery at a predetermined magnitude of pressure.

3. A fuse cutout being comprised of a fuse tube, a fuse tube end casting, a cap and a disc; one end of said fuse tube end casting being secured to one end of said fuse tube; the other end of said fuse tube end casting having a peripheral recess on the outer diameter thereof; said disc having a cylindrical extension; one end of said disc cylindrical extension being positioned in said peripheral recess between said fuse tube' end casting and said cap; said cap having a hollow cylindrical shape and being positioned external to and concentric with said fuse tube end casting; one end of said cap being removably secured to said fuse tube end casting and providing a friction force to secure said disc in position between said fuse tube end casting and said cap and permitting said disc to enclose said one end of said fuse tube, the other end of said disc cylindrical extension extending axially adjacent to and beyond the other end of said cap; said last mentioned disc cylindrical extension providing a barrier protection for said cap to prevent hot exhaust gases associated with current interruption in said fuse tube from damaging said cap and thereby permitting said cap to be reusable; said disc being designed to shear around the periphery at a predetermined magnitude of pressure within said fuse tube.

4. The device of claim 2 which further includes a fuse link and a fuse link button; said fuse link button being operatively connected to said rupturable disc; said fuse link button applying said predetermined magnitude of pressure during fault current conditions.

5. The device of claim 2; said rupturable disc having a central extension constructed to threadably engage the end of a threaded fuse link button, said central extension defining a reduced section about said periphery of said rupturable disc for allowing said shearing around said periphery.

References Cited in the file of this patent UNITED STATES PATENTS 1,294,621 Conrad Feb. 18, 1919 1,852,104 'Bowie Apr. 5, 1932 2,074,538 Conrad Mar. 23, 1937 2,135,164 Brock Nov. 1, 1938' 2,337,938 Serfiing et al Dec. 28, 1943 2,459,691 Earle et al. Jan. 18, 1949 2,583,440 Oxley et al Jan. 22, 1952 2,702,842 Jepsen et al Feb. 22, 1955 

